1. Field of the Invention
Genetic evolution has afforded an extraordinary array of biological capabilities in nature. Various organisms and cells achieve these different functions by producing a wide variety of proteins, many of which can in turn produce a wide variety of non-proteinaceous molecules. These naturally occurring compounds can interact to modify their environment in countless ways.
It is known that certain soil microorganisms are beneficial to plant growth through the production of growth hormones, antibiotic substances which kill harmful soil microorganisms, and by aiding in the uptake of nutrients by plants. In particular, it has been found that certain fluorescent strains of the genus Pseudomonas enhance root crop production through the production of fluorescent siderophores which confer a competitive advantage on the Pseudomonas and inhibit the growth of competing deleterious microorganisms.
Siderophores are low molecular weight compounds which are capable of sequestering or chelating iron (Fe.sup.+3) and acting as transport agents in supplying iron to the microorganism which produce them. While virtually all aerobic and facultative anaerobic microorganisms are able to produce siderophores under low iron stress, fluorescent pseudomonads produce particularly effective siderophores which act to reduce the availability of iron to other microorganisms resulting in the inhibition of disease-inducing microorganisms.
It would therefore be desirable to be able to confer on certain beneficial microorganisms the ability to preferentially compete for growth with other deleterious microorganisms in the root sphere (rhizosphere) of root crops such as potatoes, radishes, sugar beets, and the like. In particular, it would be desirable to be able to enhance the siderophore-producing capability of microorganisms which already display plant growth promoting activity.
2. Description of the Prior Art
A number of papers have been published concerning the ability of specific strains of fluorescent Pseudomonas to produce fluorescent siderophores and enhance the growth of certain root crops. See, for example, Kloepper and Schroth (1981), Phytopathology 71:1020-1023; Kloepper, et al. (1980) Curr Microbiol., 4:317-320; and Kloepper, et al. (1980) Nature, 286:885-886. The structure of ferric pseudobactin, a siderophore obtained from a particular strain of fluorescent Pseudomonas, has been determined by Teintze, et al. (1981) Biochemistry, 20:6446-6457. Other articles of interest include Meyer and Abdallah (1978) J. Gen. Microbiol., 107:319-328; Meyer and Hornsperger (1978) J. Gen. Microbiol., 107:329-331; and Misaghi, et al. (1982) Phytopathology, 72:33-36.